tests: drop old unittest.main logic

We use pytest now which doesn't need this boilerplate.

Change-Id: Ib71d90b3f1669897814ee768927b5b595ca8d789
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/354355
Reviewed-by: Josip Sokcevic <sokcevic@google.com>
Tested-by: Mike Frysinger <vapier@google.com>

tests/test_git_trace2_event_log.py

@@ -385,7 +385,3 @@ class EventLogTestCase(unittest.TestCase):
     # Check for 'start' event specific fields.
     self.assertIn('argv', start_event)
     self.assertIsInstance(start_event['argv'], list)
-
-
-if __name__ == '__main__':
-  unittest.main()